Sub coatings for bonding photographic emulsions to resinous supports



United States Patent 3,320,191 SUB COATHNGS FOR BONDING PHOTOGRAPHICEMULSHONS TO RESlNOlUS SUPPORTS George R. Secrist, Rochester, N.Y.,assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of NewJersey No Drawing. Original application Jan. 5, 1961, Ser. No. 80,759,now Patent No. 3,212,897, dated Oct. 19, 1965. Divided and thisapplication May 24, 1965, Ser. No.

asasas 2 Claims. (Cl. zen-4;

This is a division of application Ser. No. 80,759, filed Jan. 5, 1961.

This invention concerns a process for subbing hydrophobic surfaces, moreparticularly subbing surfaces to provide adhesion for photographicemulsions.

Waterproof coatings of paper, fabrics and other absorbent materials arewell known. Various waxes have been used to impart water resistance byheating the wax treated material so that the wax permeates theinterstices of the material. In addition, various synthetic resins havebeen used commercially especially to treat fabrics in the clothing andweaving industries. Photographic paper has often been made waterresistant by coating with a cellulose lacquer, but this process isunsuitable in certain instances for general paper mill use due to thevolatile solvents used and resultant hazards.

The above methods have been found generally unsatisfactory in making awater-resistant paper which may be used photographically, and which iscompatible with photographic emulsions, dyes and processing chemicals.For instance, the use of a wax treatment may cause a gelatin emulsion topeel from the paper. Other treatments such as resin coatings fromsolvent solutions or hot melts permit absorption of dyes into the papercoating resulting in staining and other objectionable after effects. Ithas also been found that some of the water-resistant surfaces permitretention of processing chemicals in the paper which later affect thephotographic images.

Accordingly, it is desirable to have a photographic paper base which iseither completely or partially resistant to water and particularly tothe processing solutions in which the paper is immersed. Such papercould be rapidly processed without retention of the chemicals in thebase and could be squeegeed dry for immediate use. For instance,partially resistant stock might be sufiiciently temporarily resistant towater or photographic processing solutions to permit contact with asheet wet with water or chemicals for a few seconds without sufiicientwetting of the stock to cause cockle and mottle or similar defects andyet have a water resistance balanced in such a manner as to be receptiveto the transfer of a gelatin image.

Because of the more or less hydrophobic nature of these materials, it isusually necessary to overcoat them with subbing layers which willsatisfactorily bond the hydrophilic photographic gelatin emulsion to thebase.

The degree of emulsion adhesion necessary is fairly high considering themethods used in processing photographic materials. For instance, thesematerials are subjected to alkaline developing baths, acid fixingsolutions, and washing. Under certain conditions, mechanical processessubject the paper to unusually severe conditions of temperature, pH andfriction which require a high degree of adhesion to prevent the emulsionlayer from picking, stripping or peeling from the base.

I have found a subbing composition which is unique in providingexcellent emulsion adhesion to certain thermoplastic resinous coatingsapplied from dispersions on paper supports.

One object of this invention is to provide a subbing composition forcausing photographic emulsions to adice here to certain thermoplasticresinous coatings. Another object is to provide a photographic elementconsisting of a water-proof paper, a subbing composition, and aphotographic emulsion. A further object is to provide a unique subbingcomposition. Other objects will be apparent from the followingdescription of my invention.

I have discovered that a subbing compoition composed basically ofcasein, polystyrene latex, and gelatin has the property of providinggood adhesion for a photographic emulsion on thermoplastic resinousbases such as those provided from styrene-butadiene copolymers, acrylicresins, polystyrene-styrene:butadiene latex coatings, polystyrenecoatings, treated polyethylene coatings, and the like. This material mayalso be used on supports which are not normally considered ashydrophobic such as those listed above including paper, celluloseacetate, and the like. The optimum solids ratio layer is 60:20:20 oflatex, casein and gelatin but these proportions can be varied within 5%without sacrificing adhesion. However, the degree of adhesion obtainedthrough the use of any two of these constituents or of proportionsoutside the 5% limits is decidedly inferior to the combination of allthree in the above proportions.

The casein is alkaline-solubilized prior to addition with an alkali,preferably about 6-8% ammonium hydroxide. The amount of ammoniumhydroxide or other alkali is only important with respect to the final pHand its effect on coating viscosity, gloss, and the like.

The preferred grades of gelatin are those most efficiently cross-linkedwith formaldehyde or other hardeners, although other grades may be used.

Sub coverages of from 0.5-3.0 g./m. may be *used.

Coatings may be applied by hopper, air knife, spray or any othertechnique by which the subbing dispersion can be evenly spread over theresinous base.

Various wetting agents may be used such as those sold under the namesTriton X (alkyl .aryl polyether alcohol), Duponol ME (sodium laurylsulfate) and the like. Other compositions may be added which are helpfulin obtaining a good final product but which are not necessary for theoperation of our invention. For instance, chelating agents such as thesodium salt of ethylene diamine tet-raacetate, (Versene regular,Sequest-rene NA 4, Nullapon BF-78) and the like may be added to deionizethe water. Sodium 'meta-borate may be added in an amount from 26% toimprove the gloss under certain conditions.

In some cases, adhesion can be further improved through addition to thesub of certain water miscible solvents which act as softening, swelling,tackifying or partial solubilizing agents for theresinous material ofthe layer being subbed and/or the sub dispersion. Many such solvents areavailable and include dimethyl formamide, tetrahydrofuran, methylethylketone, cyclohexanone, propylene carbonate, ethylene glycol monoethylether acetate (Cellosolve acetate), n-methyl pyrrolidone and others.that the solvent used be able to be volatilized at the temperature usedin drying so that the finished coating is not sticky or tacky.

The following general ranges are my preferred concentrations of theadditional components that have worked satisfactorily:

Percent Chelating agent (on total weight) 0.2-0.5 Surfactant (on totalweight) 0.05-05 A heat treatment may be used at a temperature of 240-280F. for 10-20 seconds, but is not necessary.

One requirement of this technique is The following examples are intendedto illustrate our invention but not to limit it in any way.

EXAMPLE 1 A sample of photographic baryta coated paper stock was coatedon both sides with a 15 g./m. coating of 50:50 solids blend ofpolystyrene latex and styrenezbutadiene (60:40) latex. This coated paperwas very hydrophobic to water and showed a moisture pickup (Cobb test)of approximately 0.02 g./ 100 cm. after 8 minutes exposure to water at70 F. A 1.0 g./rn. sub coating of the following composition was thencoated over the face side resinous layer.

Material: Weight, gms. Water 907.9 Chelating agent 2.5 Wet-ting agent1.5 Sodium meta-borate 2.0 Casein 7.6 Polystyrene latex (32.5% solids)70.0 Gelatin 7.6 40% formaldehyde 0.9

The sub coating was dried by passing the paper first through an airdrier at 160-180 F. for l-l5 sec. and then in front of a bank ofinfrared heaters at 240280 F. for -20 sec. The paper was then coated onthe face side with a suitable photographic gelatin-based emulsion, anddried. When processed, no evidence of emulsion frill was noted. The samepaper without the sub layer showed a complete sloughing off of theemulsion during processing.

When the same latex coated base was subbed with a 1.0 g./m. sub coatingcomposed of equal parts (by solids weight) of a resin latex mixture ofpolystyrene resin latexstyrene butadiene resin latex combination (45 :55by solids weight) and gelatin, adhesion was not considered passable--anobjectionable amount of emulsion coating could be rubbed away.

EXAMPLE 2 A sample of baryta coated photographic paper was coated asdescribed in Example 1 except that the waterproof resinous support layerwas made of a blend of polyacrylic resin latexes. This layer was morehydrophobic than the polystyrene-styrene butadiene latex coating butwhen subbed, sensitized, and processed, showed the same excellentemulsion adhesion.

EXAMPLE 3 A sample of baryta coated photographic paper was cotaed on theface side with a 2.0 g./m. coating of a blend of two styrenezbutadienelatexes with casein to provide a water resistant base (Cobb moisturepickup was 0.04 g./ 100 cm. in one minute). A 1.0 g./m. layer of thecomposition described in Example 1 was applied over this resin layer,dried as previously described, and coated with a suitable photographicgelatin emulsion. When tray processed by hand and also when mechanicallyprocessed under extreme temperature, pH and friction conditions,emulsion adhesion was excellent. Without the subbing layer, this samepaper showed a complete stripping of the photographic emulsion from thebase.

EXAMPLE 4 A sample of baryta coated photographic paper was coated on theface side with a 2.0 g./m. coating of a blend of polystyrene latex andcasein. A 1.0 g./m. layer of the sub described in Example 1 was appliedover this water-resistant layer, dried, and coated with a suitablegelatino silver halide emulsion. Emulsion adhesion was excellent. Anunsubbed sample having the same waterresistant coating showed very pooradhesion.

4 EXAMPLE 5 A sample of photographic paper stock was coated with apolyacrylic latex. This was then tub sized with the sub compositiondescribed in Example 1 and emulsion coated. Normal processing showedgood emulsion adhesion for the subbed base and poor adhesion for asimilar sample when unsubbed.

EXAMPLE 6 A baryta coated photographic paper stock was coated on theface side with 2.0 g./m. of a blend of two styrenefibutadiene latexeswith casein to provide a water resistant base (Cobb moisture pickup=0.04g./ cm. 1 min. using water at 70 F.). A 1.0 g./m. sub coating of thefollowing composition was applied over this resin layer:

Grams Water 931.4 Tetrasodium salt of ethylenediamine tetra-acetic acid2.5 Sodium alkyl polyether 0.75 Anionic alkyl aryl polyether sulfonatesurfactant 0.75 Na PO 2.0 Casein 9.5 Unplasticized polystyrene latex(49%) solids 46.5 Gelatin 5.7 Formaldehyde (40%) 0.9

1 4 solids.

This coating was dried, coated with a suitable photographic emulsion andtray tested as described in Example 1 showing excellent emulsionadhesion. When processed mechanically and continuously under conditionsof high temperature (100-120 F.), high pH (lO-ll), and unusual friction,emulsion adhesion was also excellent. Without the sub layer, this samepaper showed a complete stripping of the photographic emulsion from thebase.

EXAMPLE 7 A baryta coated photographic paper stock was coated with 10g./m. of a blend of 2-ethylhexyl acrylatezstyrene (54:46) latex withstraight polystyrene latex in a latex solids ratio of 43:57. Thiscoating was considered extremely hydrophobic showing a Cobb moisturepickup of 0.01 g./l00 cm. /8 min. using water at 70 F. This base wasthen hopper coated with a 1.0 g./m. sub of the following composition:

Grams Water 882.0 Tetrasodium salt of ethylenediamine tetra-acetic acid2.5 Sodium alkyl polyether 1.5 N'a2B204-4H2O 1 Casein 7.6 Unplasticizedpolystyrene latex (49%) solids 46.5 Gelatin 7.6 Formaldehyde (40%) 0.8Dimethyl form-amide 50.0

1 4% solids.

EXAMPLE 8 A photographic paper stock was coated on both sides byextrusion with a low-density type of polyethylene, with a resultingwater resistance equal to or better than that described in Example 1.The polyethylene surface was treated on the face side by electronbombardment (Tesla coils) to a degree that the surface was readilywettable with water. This treated surface was then subbed as describedin Example 1 except that the coating was air dried at 135-150 F. with nosubsequent radiant heat treatment. After photographic emulsion coating,tray processing frill tests showed satisfactory emulsion adhesion usingthe normal sub formula and excellent adhesion with (1) the addition of5% of either dimethyl formamide, tetrahydrofuran, or cyclohexanone or(2) substitution for formaldehyde of an equal amount of amine typehardener.

EXAMPLE 9 A baryta-coated photographic paper stock was coated with 12g./m. of a polyvinyl acetate-polyvinyl stearate (85:15) latex and showedwaterproofness equivalent to a Cobb test moisture pickup of 0.02 g./100cm. 8 min. When subbed, dried, sensitized, processed, and tested as inExample 1, this base showed satisfactory emulsion adhesion.

The preceding examples are intended to show the successful use of myinvention in achieving satisfactory adhesion of photographicgelatin-based emulsions to a number of radically diiferent resinouscoatings. Many other polystyrene, styrene:butadiene, polyacrylic,polyvinyl chloride and polyvinyl acetate homopolymer and copolymerlatexes have been subbed successfully.

This sub is effective for coating over thermoplastic material depositedfrom solutions or from latexes. It may also be coated over such aresinous surface when the surface has been deposited or coated onvarious supports such as resinous supports, paper, leather, syntheticfibers, or the like.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be elfected within the spirit and scope of theinvention as described hereinabove and as defined in the appendedclaims.

I claim:

1. An aqueous composition for thermoplastic resinous surfaces consistingessentially of 65% by weight polystyrene resin latex, 15-25% by weightcasein, and 15- 25% by weight gelatin, solids basis.

2. A subbing composition for thermoplastic resinous surfaces consistingessentially of an aqueous dispersion of 55-65% by weight polystyreneresin latex, 15-25% by weight casein and 1525% by weight gelatin, on asolids basis, and a water miscible solvent selected from the groupconsisting of dimethyl formamide, tetrahydrofuran, methylethyl ketone,cyclohexanone, propylene carbonate, ethylene glycol monoethyl etheracetate and n-methyl pyrrolidone.

References Cited by the Examiner UNITED STATES PATENTS 2,731,435 1/1956Johnson et a1. 2608 2,875,055 2/1959 Griggs et al. a 117-34 2,912,39311/1959 Stilbert et al. a 26017.4 2,971,876 2/1961 Phair 1171383,021,214 2/1962 Murphy et al. 9685 WILLIAM H. SHORT, Primary Examiner.

E. M. WOODBERRY, Assistant Examiner.

1. AN AQUEOUS COMPOSITION FOR THERMOPLASTIC RESINOUS SURFACES CONSISTINGESSENTIALLY OF 55-65% BY WEIGHT POLYSTYRENE RESIN LATEX, 15-25% BYWEIGHT CASEIN, AND 1525% BY WEIGHT GELATIN, SOLIDS BASIS.